The present invention relates to compositions comprising oil-soluble scale inhibitors and their use in inhibiting oil field scale formation. More particularly, the present invention relates to compositions comprising an acid form of a known scale inhibitor and a tertiary alkyl primary amine. The compositions of the present invention may be used in inhibiting oil field scale formation. Such methods of use have many advantages over conventional techniques of inhibiting oil field scale, one benefit being a decrease in the period for which production of oil is suspended or reduced during treatment, and reducing the expense of the descaling operation. Furthermore, the compositions may be used in conjunction with other agents such as anti-corrosion agents, wax inhibitors and asphaltene inhibitors.
When a well bore is initially drilled in an oil field, the oil extracted is usually xe2x80x9cdryxe2x80x9d, being substantially free of aqueous impurities. However, as the oil reserves dwindle, a progressively greater quantity of aqueous impurities becomes mixed with the oil. Changes in formation physical conditions during the production cycle as well as mixing of incompatible waters (i.e. sea water and barium or strontium containing formation waters) can cause scaling in any part of the production system. Scale that occurs in the production system can result in a significant loss in production and associated revenue.
One problem with scale formation in large industrial wells is the formation of scale on the equipment used to extract oil from the field, particularly on the interior surfaces of production tubing and at the perforations in the wall of the casing itself. At the well head, the sub-surface safety valve is also susceptible to damage caused by scale formation.
There are several conventional techniques to counter the problem of oil field scale formation, all of which bear significant disadvantages. The technique of xe2x80x9cdownhole squeezingxe2x80x9d is commonly used, wherein inhibitor chemicals in aqueous solution are injected into the near-wellbore area. A typical squeeze in a vertical well will comprise a preflush, a squeeze pill and an overflush treatment, before the well is returned to normal function. The preflush, typically comprising a mixture of surfactant/demulsifier solution, stops the formation of emulsions that would block the perforation pores and may wet (with water) formation surfaces. The squeeze pill itself typically involves injection of inhibitor as a 1-20% solution in water, causing saturation of the matrix in a radial area around the well. The overflush comprises a displacement of the squeeze pill that propels the chemical front in a wider circumference around the well bore so that a significant surface of rock matrix is exposed to the inhibitor compound.
When the pressure applied down the well is reversed, about 30% of inhibitor chemical is often immediately flushed from the rock. The remaining solution adsorbs to the rock surface and acts to inhibit scale formation by constant treatment as fluid passes through the rock formation into the well conduit. However, over time the inhibitor is gradually washed from the rock surface as oil production continues until a further descaling treatment is required.
Various techniques have been used to try to increase the proportion of chemical that adsorbs to the rock. For example, the chemical can be xe2x80x9cshut inxe2x80x9d for a period of time with the expectation that the greater period of exposure to the rock surface might increase the degree of absorbency of inhibitor. However, this leads to an increase in the time for which a well is not in production and additionally is not considered to be particularly effective.
A further problem with downhole squeezing is that the aqueous solutions of scale inhibitor tend to change the wettability of the rock; due to its immiscibility with water, oil will not flow through xe2x80x9cwater-wetxe2x80x9d rock. Once wet, the water permeability of the rock has been changed, sometimes permanently, so that a water channel may eventually open up into a water pocket, leading to the so-called xe2x80x9cwater coningxe2x80x9d effect wherein a well is irreversibly damaged. Such a well will never again return to full productivity and new perforations need therefore be sunk in order to economically extract oil from the field.
Another problem with conventional techniques of treatment derives from the fact that aqueous solutions are usually more dense than the crude oil in the field. Consequently, once an aqueous solution of oil scale inhibitor has been used to treat a well, there is insufficient pressure support in the field for the well to flow naturally after treatment has finished. Consequently, the well must often be xe2x80x9cgas-liftedxe2x80x9d back into production using coil tubing until the natural oil pressure is sufficient to drive the flow once again. However, the gas lift facilities may not always be available and it is expensive and time-consuming to rig up temporary facilities.
If continuous injection facilities are available, the inhibitor compound may be applied continuously to the production stream. However, such facilities are not always feasible and are only available in relatively modern wells.
It is only now, with the advent of more advanced techniques for analyzing the process of oil extraction that the problems set out above have been appreciated. There thus exists a great need for a method of inhibiting oil scale formation that does not suffer from the disadvantages that beset conventional techniques.
Furthermore, in offshore natural gas production systems, alcohols such as methanol or ethylene glycol are often introduced into the well, well head or flow line to prevent formation of hydrates which can cause plugging problems in the same manner as scale deposition. When gas/condensate production occurs remotely from a platform via a sub-sea flow line, conventionally, chemical injection at the wellhead or downhole is supplied by an umbilical connector in which are contained a bundle of lines. It is necessary to supply scale inhibitor in a separate line because traditional scale inhibitors are generally intolerant of alcohols, to the extent that mixing of the two types of chemical causes severe precipitation problems with the scale inhibitor. However, each line is extremely costly. Accordingly, a scale inhibitor composition that is compatible with both traditional oilfield treatment chemicals and other organic solvent packages is particularly useful, since it avoids the necessity to supply the scale inhibitor separately.
According to a first aspect of the present invention there is provided a composition containing an oil-soluble scale inhibitor, said oil-soluble inhibitor comprising a scale inhibitor and a tertiary alkyl primary amine. Preferably, the composition is dissolved in a hydrocarbon or other fluid.
By oil-soluble is meant that the composition is infinitely soluble in usual hydrocarbon carriers such as diesel and kerosene. However, since scale formation in oil wells is only associated with the production of water in the well, it is essential that the scale inhibitor must be able to partition between phases so that it is water soluble in the process system or downhole and therein able to act as an inhibitor of scale formation.
Any inhibitor for which an acid form may be easily produced is suitable for use according to the present invention. Preferably, the acid form of scale inhibitor has a pH of typically less than 2.5. Scale inhibitors suitable for use in accordance with the present invention include phosphonates, acrylic co/ter-polymers, polyacrylic acid (PAA), phosphino carboxylic acid (PPCA) or phosphate esters or other traditional water based scale inhibitor chemistries. Suitable scale inhibitors are known to those of skill in the art.
In order to form a composition according to the present invention, the scale inhibitor in acid form is blended with an amine to form an oil-soluble mix. The scale inhibitor should be mixed with a tertiary alkyl primary amine, such as, for example, the tertiary alkyl primary amines marketed in the Primene(copyright) range of compounds (Rohm and Haas).
Tertiary alkyl primary amines possess several advantageous properties over other types of amines for blending with typical scale inhibitors. These advantages include the manageable reactivity of the nitrogen group that gives the chemist great control over the products generated in any reaction process. Additionally, the amines and derivatives thereof remain fluid over a wide range of temperatures and are soluble in hydrocarbon fluids such as kerosenes, diesel and HAN (Heavy Aromatic Naphthas).
The tertiary alkyl primary amine may possess one amine group or may possess multiple amino groups. Preferably, the tertiary alkyl primary amine comprises tertiary alkyl primary amines marketed in the Primene(copyright) range of compounds (Rohm and Haas), most preferably the Primene(copyright) 81-R range. The latter product comprises a mixture of amines in the C12 to C14 range.
It is envisaged that as and when new xe2x80x9cgreenxe2x80x9d amine compounds are developed that exhibit low toxicity, are biodegradable or do not accumulate in the environment, these amine compounds will be suitable for use in the present invention.
Examples of suitable scale inhibitors that are suitable for use in the compositions of the present invention include, hexamethylene diamine tetrakis (methylene phosphonic acid), diethylene triamine tetra (methylene phosphonic acid), diethylene triamine penta (methylene phosphonic acid), bis-hexamethylene triamine pentakis (methylene phosphonic acid), polyacrylic acid (PAA), phosphino carboxylic acid (PPCA) iglycol amine phosphonate (DGA phosphonate); 1-hydroxyethylidene 1,1 -diphosphonate (HEDP phosphonate); bisaminoethylether phosphonate (BAEE phosphonate) and polymers of sulphonic acid on a polycarboxylic acid backbone.
Suitable proportions of amine:scale inhibitor are those required to produce a reaction product that is infinitely soluble in nontraditional organic solvents such as those mentioned above. The precise proportions of amine to scale inhibitor used to make the composition will depend on the particular scale inhibitor, but generally will range between the ratios 100:1 to 1:3, more usually 8:1 to 1:13:2 for amine to scale inhibitor. The concentration of inhibitor in the reaction product may thus range between 10% and 50% by volume. Particularly suitable ratios are 3:2 Primene(copyright) to phosphonate, 4:1 Primene(copyright) to acrylic polymer. The below listed compositions are also effective as inhibitors of scale in oil well systems. The below listed compositions are also effective as inhibitors of scale in oil well systems. The proportions are only meant as an approximate estimate and variations around these values will be necessary depending upon the environment of the area for treatment. The proportions of scale inhibitor material for blending with the amine refers to proportions of commercially-sold inhibitor products, not proportions of the active ingredient. Most concentrated scale inhibitor commercial bases typically comprises 35-50% active solutions of scale inhibitor molecules.
To facilitate their application into a hydrocarbon production system, the scale inhibitor compositions of the invention may be supplied as a concentrate that can be diluted appropriately on site. This reduces the amount of the composition that needs to be conveyed to the site, thus making the transportation process more convenient.
The compositions may also be supplied as a specific dilution with hydrocarbon solvents such as HAN, diesel, base oil, kerosene, or condensate containing a specific concentration of oil soluble inhibitor that has been designed for a specific application. These compositions can be further blended into diesel or crude oil for use in the field.
Alternatively, the compositions may be supplied in other organic solvents not traditionally used with scale inhibitors as the primary solvent, such as methanol or isopropyl alcohol. Traditional scale inhibitors are generally intolerant of such alcohols, to the extent that they cause severe precipitation problems with the scale inhibitor.
Compositions can also be supplied as ready-made dilutions in solvent for direct use in the field, so that no additional mixing is required on site.
A composition according to the present invention may be dissolved in any hydrocarbon fluid. Preferably, the fluid is an aromatic hydrocarbon solvent such as, for example hydrocarbon fluids such as kerosenes, diesel, base-oil, HAN (Heavy Aromatic Naphtha) xylene, toluene, condensate, and crude oils. Additionally, the composition may be dissolved in other organic solvents not conventionally used as the primary solvent for scale inhibitor application, such as methanol or isopropyl alcohol.
The scale inhibitor will, of course, need to be present in the composition in a concentration effective for the inhibition of scale formation. The lowest concentration at which the scale inhibitor will be effective is termed its minimum inhibition concentration (MIC), which varies for different mineral contents of the brine water.
Another advantage provided by the compositions of the present invention is that they may be used in conjunction with hydrocarbon production treatment chemicals not conventionally combined with scale inhibitors due to their incompatibility with said scale inhibitors or with other oil-based production chemicals such as wax inhibitors, asphaltene inhibitors, corrosion inhibitors or hydraulic fluids. These chemicals include organic solvent-based production chemicals such as wax inhibitors, asphaltene dispersants and inhibitors, corrosion inhibitors, hydraulic fluids, scale dissolvers, paraffin solvents and dispersants, pour point depressants and wax fluids.crystal modifiers, demulsifiers, foamers and defoamers, gas hydrate inhibitors, biocides and hydrogen sulphide scavengers. This enables an engineer to administer a number of separate treatments in one batch, so decreasing the disruption to the working of the well and correspondingly making periodic overhaul of the well a more cost-effective process.
A particularly suitable wax inhibitor is Champion WM 1230 inhibitor and a particularly suitable asphaltene inhibitor is Champion WM1130 inhibitor. For wax inhibitor, suitable ratios include between 4:6 to 2:8 oil soluble inhibitor to wax inhibitor. Asphaltene inhibitor might be included in the following ratio; 2:1:7 of oil soluble inhibitor to wax inhibitor to asphaltene inhibitor. However, since the oil soluble inhibitor compositions of the invention are completely oil soluble, wax and/or asphaltene inhibitor can be included at any concentration above its MIC.
It has been found that the oil-soluble inhibitors of the present invention demonstrate a high affinity for heterogeneous rock and are adsorbed effectively. Dependent on the volume of oil that flows from the well during the time of operation, the effective period of action may be up to eighteen months.
According to a second aspect of the present invention there is provided the use of a composition according to the first aspect of the invention in a hydrocarbon production system. By hydrocarbon system is meant any part of the hydrocarbon production process from the wellbore area (including the rock matrix) to any facility or apparatus that makes delivery to a refinery or refinery process. Included as part of a hydrocarbon production system are surface equipment such as heater treaters, crude oil heaters, separators, manifolds, and flow control valves. Flow systems such as pipelines, whether for bulk transport or as field gathering systems, are also included as suitable targets for treatment. Other equipment suitable for treatment will be clear to the skilled worker.
Oil well systems and natural gas production systems are both included as suitable hydrocarbon production systems in which the compositions of the invention may be applied. Preferably, the composition is used in an oil well system. By oil well system is meant any part of the wellbore area (including the rock matrix) or the drill equipment.
According to a still further aspect of the invention there is provided a method of inhibiting oil scale formation in an oil well comprising introducing a composition containing oil-soluble scale inhibitor according to the first aspect of the invention in an effective amount into the environment of the well system.
It is envisaged that conventional downhole squeeze techniques will be most effective in the method of this aspect of the invention to introduce the compositions into the well bore environment as a batch treatment, although it is not intended that the method be limited to this technique. For instance, in wells where injection facilities are available, compositions according to the invention may be applied continuously to the production stream along with any other desired oil-soluble compounds such as wax inhibitors, asphaltene inhibitors and/or corrosion inhibitors.
Squeezing will typically involve the application of downward pressure on the well so that for a period of time the flow of oil effectively runs in reverse. A typical squeeze in a vertical well will comprise a preflush of around 50-150 barrels of inhibitor followed by injection into the rock matrix around the well bore in a radial area of between 200 and 1500 barrels of inhibitor. The overflush typically comprises an 8-20 foot squeeze using sea water, diesel or any other suitable fluid.
Alternative methods of introduction of the oil-soluble scale inhibitors of the present invention into the near system include the use of downhole and topside continuous injection, and gas lift treatments.
Various aspects and embodiments of the present invention will now be described in more detail by way of example. It will be appreciated that modification of detail may be made without departing from the scope of the invention.